The analysis of tubewaves or pressure waves and/or their echoes can detect a fracture bottom irregularity, or other features in a well. Several references describe the analysis of pressure wave reflections, such as US 2011/0267922, US 2012/0018150, U.S. Pat. No. 6,192,3216, and U.S. Pat. No. 7,819,188.
Noise in the well system can obscure pressure wave measurements, or require the use of higher amplitude pressure signals for an appropriate signal-to-noise ratio. The piping system resonances, as well as the pressure fluctuations from plunger pumps, can interfere with or obscure pressure signal measurements. For example, significant resonances in piping and wellbores can damage equipment and interfere with treatment operations. As another example, the pressure fluctuation of a triplex pump pumping treatment fluid at 400 rpm has a frequency of 20 Hz that can interfere with pressure wave measurements.
In the past, the treating lines on fracturing missile trailers have had resonant frequencies that were excited by the triplex pumps, producing stress fluctuations in the treating lines and eventually fatigue failures. One solution to this problem involved fitting each missile trailer inlet with one of three sizes of converging-diverging nozzles, referred to herein as sonic chokes. These chokes dissipated roughly 700 kPa (about 100 psi) at their design flow rate, and along with other design changes, made the treating lines less sensitive to fatigue damage and eliminated this class of failure.
For duplex “mud” or drilling fluid pumps, gas-filled rubber bladders have been applied to both the suction and discharge sides in an effort to reduce pressure fluctuations associated with single and double acting pumps, which produce much larger pulsations than the triplex pumps commonly employed in portable oilfield pumping. While effective where they can be used, these dampers are impractical to apply to severe services where significant abrasives, high pressure, and/or aggressive fluids are employed. The available dampers are only rated up to 70 MPa (10,000 psi), and would fail rapidly when exposed to the complex acids and hydrocarbons employed in fracturing. Further, constructing such a device in a 100 MPa (15,000 psi) rating would entail a radical increase in wall thickness.
Moreover, gas-filled rubber bladder systems are very limited in the range of the ratio of pumping pressure to gas pre-charge that they can support. For example, a 3:1 ratio between the pre-charge pressure and the maximum reliable operating pressure represents a good ratio; in which case a damper that will be pressure tested to 100 MPa (15,000 psi) is charged to at least 3.5 MPa (5,000 psi). With this pre-charge, however, the damper will have no effect at all below 3.5 MPa (5,000 psi), whereas the optimum charge for damping is around 80% of the operating pressure for a bladder type damper. Moreover, the bladders require adjustment from job to job, rather than being set up and left in service. Thus, such a system has significant limitations that make it impractical for most fracturing operations.
The industry has an ongoing need for the development or improvement of noise reduction methods and systems to facilitate pressure wave measurements.